Method and apparatus for applying a gel

ABSTRACT

A rotatable vacuum chamber receives an optical connector having an output face on which an optical gel is applied substantially without entrapped air. Opposite the output face is placed a gel dispenser with its opened nozzle pointing towards the output face. Uncured gel components contained in the dispenser are outgased prior to application of the gel on the output face while a vacuum is maintained in the chamber. Outgasing takes place at a first chamber orientation with the nozzle pointing upwards through which the outgasing air ventilates. The gel is applied at a second chamber orientation where the output face is horizontal and upwards pointing. Immediately following the gel application, the vacuum is unmade to prevent cooking of the mixed and uncured gel. A glass plate is then pressed against the applied fluid gel.

CROSS REFERENCE

This application cross-references the concurrently filed U.S. patentapplication for “Apparatus for Holding a Fiber Array” of Steven Nasiri,Janusz Liberkowski, Eddy Chen and Jeff Jarfa, which is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to method and apparatus for applying a gelin vacuum. Particularly, the present invention relates to method andapparatus for applying an optical gel on an output face of an opticalconnector.

BACKGROUND

No Prior Art?

In the field of optical data communication, increasingly complex devicesare developed with ever growing numbers of integrated and simultaneouslyoperated optical fibers. Such a devices, like for example, opticalswitching fabric integrate more than thousand optical fibers and performsimultaneous switching operations between the individual fibers. Inorder to efficiently handle such a large number of integrated fibers,special constructive efforts are necessary. Sub components like, forexample, optical connectors are designed to tightly combine and holdfibers such that their ends are planar arrayed and parallel oriented onan output face. Information carrying light beams propagate towards andaway from the fiber ends embedded and coplanar polished together withthe output face. The efficiency of the beam propagation in and out ofthe fiber ends is highly dependent on the surface quality of the outputface. Several fabrication steps are performed to insert and bond thefiber ends and then grind and polish the output face.

During the lifetime of an optical switching fabric, the output faceneeds to be protected against humidity to prevent corrosive damage. Anoptical connector may be designed to hermetically seal the output face.For that purpose, a glass plate may be placed on top of the output face.In such a case, the gap between the output face and the glass plate isfilled with an optical gel that has substantially the same refractiveindex as the glass plate. In that context it is referred to theconcurrently filed Patent Application for “Apparatus for Holding a FiberArray” of Janusz Liberkowski and Steven Nasiri. While applying the geland sealing the gap between the glass plate and the output face it iscrucial that entrapped air bubbles are avoided.

Conventional methods where the gel is applied under atmospheric airpressure have proven insufficient. There are three main reasons forthat. Firstly, microscopic air bubbles tend to adhere to the output facewhile the gel is applied. The air bubbles appear to adhere at theboundaries between the four materials present at the output face, whichmay be silicon of the insert in which the fiber ends are inserted, glassof the fiber, glass plate end and epoxy with which the fiber end isbonded. When the gel is pressed between surface of the silicon andsurface of the glass, air bubbles are squeezed out from the gel layer.

Secondly, the unmixed gel components themselves may contain entrappedair. And thirdly, immediately prior gel application, the individual gelcomponents are mixed to initiate the chemical reaction that causes thecuring of the gel. During the mixing, air may also be entrapped.

These three reasons to the contrary, the mixed gel needs to be keptunder atmospheric pressure to avoid a well-known cooking of the gel inthe vacuum where gas bubbles are formed within the gel.

Therefore, there exists a need for a special method and apparatus forapplying a gel to a face and to seal a gap between two faces withoutentrapped air bubbles and to avoid cooking of the gel. The presentinvention addresses this need.

SUMMARY

In the present invention, eventual entrapped air is outgased from theunmixed gel components before the gel components are mixed and appliedonto the output face. In addition, the mixing of the gel and itsapplication on the output face is performed under substantially reducesair pressure. As a consequence, entrapped air bubbles are avoided.Immediately following the mixing and application of the gel atmosphericpressure is reapplied to the gel to prevent eventual cooking of it.

The gel is applied in a fashion such that it forms a slightly raiseddome shape with the top of it being at a central area of the outputface. In a following step, where the glass plate is brought into contactwith the uncured gel on the output face, it touches first the gel at thecentral area of the output face. The glass plate is then continuouslyforced against the output face and the contact area between the gel andthe glass plate enlarges in radial direction. At the same time, excessgel is forced out of the gap flushing the contact area between glassplate and gel. In that way, also the contact area between the glassplate and the gel is kept free of entrapped air bubbles.

After the initial steps of outgasing the unmixed gel, the gel is mixedand applied in vacuum. For that purpose, the optical connector is placedand fixed together with a commercially available gel dispenser in aspecifically configured rotatable vacuum chamber. The gel dispenser haspreferably two compartments where two unmixed gel components arecontained. The compartments terminate in a nozzle where the gelcomponents are mixed and dispensed. The gel dispenser is placed relativeto the optical connector such that the nozzle is pointing at a centrallocation of the output face.

After the work piece and the gel dispenser are fixed, the vacuum chamberis closed and a vacuum is applied for a time period sufficient for theoutgasing. During that period, the vacuum chamber is rotated into afirst orientation where the nozzle points upwards and the output faceconsequently points downwards.

Once the outgasing of the gel components is completed, the gel isapplied on the output face. A piston like actuator reaches from outsidethrough the housing of the vacuum chamber such that the gel dispensercan be actuated while maintaining the vacuum. During gel application,the vacuum chamber is rotated into a second orientation where the outputface points upwards and the nozzle downwards.

Immediately following the gel application, the vacuum is unmade and theglass plate is pressed onto the gel as described in the above. Duringcuring of the gel the glass plate is fixedly held relative to the outputface.

The method is relatively simple and allows an efficient fabrication ofthe desired sealed output face. Adapting the vacuum chamber for anintegration of a commercially available gel dispenser allows short setupperiods.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates schematically the rotating vacuum chamber togetherwith the work piece and the gel dispenser in a first orientation duringoutgasing of the unmixed gel components.

FIG. 2 depicts the apparatus of FIG. 1 in a second orientation duringgel application.

FIGS. 3 a, 3 b show two stage of making the sealed gap between the glassplate and the output face.

FIG. 4 is a block diagram illustrating the steps included in sealing theoutput face with a glass plate.

DETAILED DESCRIPTION

Referring to FIG. 1, the main components and apparatus for practicingthe method of the present invention are described. A main apparatus is aspecially configured, rotatable vacuum chamber 10 that pivots around thehinges 11. The vacuum chamber 10 features a work piece holder 12 forfixedly holding a work piece 20 having a gel application face 21. In thepreferred embodiment, the work piece 20 is an optical connector and thegel application face 21 is an output face having a number of coplanarfiber ends terminating on it.

The vacuum chamber 10 also features a dispenser holder 14 for fixedlyholding a gel dispenser 30. The gel dispenser 30 has a nozzle 31, twocompartments for separately containing unmixed gel components 33, 34,and a bridge actuator 36 for combined actuating two separate pistons 35.Each of the pistons 35 slides along one compartment for forcing the gelcomponents 33, 34 towards and through the nozzle 31 when a force isapplied to the bridge actuator 36. The gel dispenser 30 may be acommercially available dispenser sold by Nye Optical Product under thename OCK-433. Both holders 12, 14 are configured to easily insert andfixate the work piece 20 and the gel dispenser 30 such that the nozzle31 is pointing at a central area of the gel application face 21. In thepreferred embodiment, where an optical gel OCK is applied, the distanceof the nozzle's 31 tip to the gel application face 21 is in the range of1 mm.

The vacuum chamber 10 further features a dispenser actuator 13 forremotely actuating the gel dispenser 30 from outside the vacuum chamber10. In its simplest configuration, the dispenser actuator 13 is amechanically operated rod sliding along a sealed guide 15 in a directionsubstantially collinear to an actuation direction of the fixed geldispenser 30. In that way, a force F1 applied at the outside end of thedispenser actuator 13 is transmitted onto the bridge actuator 36 suchthat the unmixed gel components 33, 34 are forced out of theircompartments.

The vacuum chamber 10 may also have a lid 17 for accessing and sealingthe vacuum chamber's 10 interior. The lid 17 may have any well-knownconfiguration as may be appreciated by anybody skilled in the art. Whilethe lid 17 is closed, the interior of the vacuum chamber is sealed andmay be evacuated by a connected vacuum generator 16. The vacuumgenerator 16 is placed in proximity of the vacuum chamber 10 andconnected via a well-known flexible element for transmitting a vacuumsuch as a vacuum hose 18. The vacuum hose is configured and connected tothe vacuum chamber 10 for an uninhibited rotation of the vacuum chamber10 of at least 180 degrees around the hinges 11. The vacuum generator 16may be placed stationary and not participate in the rotation of thevacuum chamber 10. The vacuum generator 16 may be a commerciallyavailable product.

In the preferred embodiment, the work piece 20 in its configuration asthe optical connector, a number of optical fibers 22 may loosely extendfrom the work piece 20 at the opposite end of the gel application face21. In such case, the vacuum chamber 10 may provide sufficient space forreceiving the extending optical fibers 22.

In the preferred embodiment, the vacuum chamber 10 may be made of a tubethat extends concentrically relative to the assembled work piece 20. Thetube may be configured to provide visual access to the fixed geldispenser 30 and the gel application face 21. In its simplestconfiguration, the tube may be of transparent material.

Now, referring to the block diagram of FIG. 4, the method of the presentinvention will be described in detail. In a first step 51, the workpiece 20 is placed and fixed in the holder 12. In the preferredembodiment where also the fibers 22 need to be inserted, the vacuumchamber 10 may be brought into an orientation such that the work piece20 may be inserted with the fibers 22 hanging downwards.

In a following step 52, the gel dispenser 30 is placed and fixed in theholder 52 after it has been brought into operational configuration,which may include removing a well-known seal of the nozzle 31. In thepreferred embodiment, where highly liquid gel components 33, 34 areused, the vacuum chamber 10 may be set in a first orientation such thatthe gel dispenser is placed and fixated while the opened nozzle 31 ispointing upwards. In that way, gel motion and eventual air entrapment iskept to a minimum.

Next, during step 53 the lid 17 is closed and the vacuum chamber 10sealed. Then, the vacuum generator 16 is activated and a vacuum in therange of 30 in of mercury or about 100 kPa is applied.

In step 54, the established vacuum is maintained for a period sufficientfor outgasing air eventually entrapped and dissolved under atmosphericpressure in the unmixed gel components 33, 34. In the preferredembodiment, where the above-mentioned type gel dispenser 30 is utilized,the vacuum is maintained for a period in the range of 24 hours. Duringthe outgasing, the vacuum chamber 10 is kept in a first orientationwhere the nozzle is pointing upwards. In that way, air that rises in thegel components 33, 34 may ventilate through the open nozzle 31.

After the outgasing is completed, an optional step may be performedbefore rotating the vacuum chamber 10 into a second orientation andapplying the mixed gel. In the preferred embodiment, where a highlyliquid optical gel is applied, the gel dispenser 30 may be remotelyactuated via the actuator 13 such that the gel components 33, 34 areforced up to the nozzle's 31 tip. In that way, the entire cavity of thegel dispenser 30 is filled with gel, which may be advantageous wheninitiating the application of the highly liquid optical gel as isdescribed in the below under step 56.

In step 55, the vacuum chamber 10 is rotated into the secondorientation, where the nozzle 31 is pointing downwards and the gelapplication face 21 is substantially horizontal and pointing upwards.

Immediately following is step 56 where the gel components 33, 34 arecontinuously mixed in the nozzle 31 and centrally dispensed onto the gelapplication face 21. The step 56 is schematically illustrated in FIG. 2.During step 56, the force F1 is applied on the actuator 13 andtransmitted onto the bridge actuator 36 and the pistons 35. The gelcomponents 33, 34 are pressurized and forced through the nozzle 31 ontothe face 21 where the mixed and uncured gel 32 forms a dome like fluidlayer. In the preferred embodiment, the fluid layer has a thickness ofabout 2 mm.

The application of the fluid layer is swiftly performed to minimize theperiod during which the mixed gel is exposed to the vacuum such that therisk of eventual well-known cooking of the gel is kept to a minimum. Thecooking is a result of a chemical reaction that typically requires acertain time to initiate and is substantially avoided if the vacuum istimely unmade. In the preferred embodiment, the application period ofthe above-specified optical gel is in the range of 10 to 15 min at 25°C. Increase of the temperature will significantly shortening set time asit may be appreciated by anybody skilled in the art.

Now, the following step 58 is described by referring to FIGS. 3 a, 3 b.Once the uncured gel 32 covers the face 21, the gel application iscompleted and the vacuum chamber 10 opened. After the dispenser 30 isremoved and a second work piece 40 is brought with its bottom face 41into plane parallel orientation to the face 21 and contacted with theuncured gel 32. Due to the dome like shape of the uncured gel 32, thebottom face 41 initially contacts the uncured gel 32 in the central areaCA. As the bottom face 41 is pressed towards the face 21 via the forceF2, the contact area CA enlarges concentrically. In that way, the gapbetween the bottom face 41 and the face 21 is filled and sealed by theuncured gel 32 substantially without any entrapped air bubbles. Whilethe bottom face 41 is moving towards the face 21, excess gel islaterally squeezed out of the continuously narrowing gap.

In the preferred embodiment, the second work piece 40 is a glass plateand the uncured gel 32 is an optical gel. Once the optical gel is cured,it has a refractive index substantially matching that of the glassplate. The glass plate may receive the force F2 via an external housingat which the glass plate may be attached. The force F2 may be providedby fastening screws in combination with elastic members configured inconjunction with the viscosity of the optical gel and the size of theface 21 resulting in a predetermined gap thickness 32 h. For theabove-mentioned type optical gel and an exemplary size of the face 21 of30×40 mm, a gap thickness 32 h in the range of 10 to 400 μm is providedby applying force F2 in the range of 0.49 N to 1.96 N.

In an optional final step 59 and once the desired gap width is reached,the position between first and second work piece 20, 40 is fixed duringthe curing of the gel.

Accordingly, the scope of the invention described in the specificationabove is set forth by the following claims and their legal equivalent:

1-5. (canceled)
 6. A method for sealing a gap between a first face and asecond face substantially free of entrapped air, said method comprisingthe following steps of: a. placing a first work piece having said firstface in a rotatable vacuum chamber such that said first face is pointingdownwards; b. placing a gel dispenser in said vacuum chamber such that adispensing nozzle is pointing upwards at a central area of said firstface, said gel dispenser containing unmixed gel components; c. sealingsaid vacuum chamber and applying a vacuum; d. maintaining said vacuumfor an outgasing of said unmixed gel components through said nozzle; e.rotating said vacuum chamber together with said first work piece andsaid gel dispenser such that said first face is pointing upwards andsaid nozzle is pointing downwards; f. remotely actuating said geldispenser such that said gel components are mixed and applied throughsaid nozzle on said first face; g. unmaking vacuum; and h. pressing asecond work piece with said second face of it substantially planeparallel towards said first face such that an excess portion of said gelapplied during step f) is concentrically squeezed out of a gap formedbetween said first face and said second face.
 7. The method of claim 6,further comprising a final step of fixedly holding said second workpiece with respect to said first work piece during a curing of said gel.8. The method of claim 6, whereby said first work piece is an opticalconnector.
 9. The method of claim 8, whereby said face is an output facehaving an embedded optical fiber end.
 10. The method of claim 8, wherebysaid gel is an optical gel.
 11. The method of claim 8, whereby saidsecond work piece is a glass plate.
 12. A method for bondingsubstantially free of entrapped air a glass plate to an optical outputface of an optical connector, said method comprising the following stepsof: a. placing said optical connector in a rotatable vacuum chamber suchthat said output face is pointing downwards; b. placing an optical geldispenser in said vacuum chamber such that a dispensing nozzle ispointing upwards at a central area of said output face, said geldispenser containing unmixed gel components; c. sealing said vacuumchamber and applying a vacuum; d. maintaining said vacuum for anoutgasing of said unmixed gel components through said nozzle; e.rotating said vacuum chamber together with said optical connector andsaid gel dispenser such that said ouput face is pointing upwards andsaid nozzle is pointing downwards; f. remotely actuating said geldispenser such that said gel components are mixed and applied throughsaid nozzle on said output face; g. unmaking vacuum; and h. pressingsaid glass plate substantially plane parallel towards said output facesuch that an excess portion of said optical gel applied during step f)is concentrically squeezed out of a gap formed between said output faceand said glass plate.
 13. The method of claim 12, further comprising afinal step of fixedly holding said glass plate with respect to saidoptical connector during a curing of said optical gel. 14-18. (canceled)